/Engine/Source/Runtime/Core/Public/Internationalization/TextLocalizationManager.h
Attempts to register the specified display string, associating it with the specified namespace and key. Returns true if the display string has been or was already associated with the namespace and key. Returns false if the display string was already associated with another namespace and key or the namespace and key are already in use by another display string.
bool AddDisplayString ( const FTextDisplayStringRef & DisplayString, const [FTextKey](API\Runtime\Core\Internationalization\FTextKey) & Namespace, const [FTextKey](API\Runtime\Core\Internationalization\FTextKey) & Key )